The present invention relates to a novel technique for producing catalysts especially useful in oxidation and ammoxidation reactions.
Catalysts found especially useful in oxidation and ammoxidation reactions are usually composed of complex compositions of mixed metal oxides. Typically, these materials are made by forming an aqueous solution or slurry of the metals in the catalyst, evaporating the water from the slurry to form a precipitate, and calcining the precipitate in the presence of oxygen at elevated temperatures to form the oxide complex.
In forming such aqueous slurries, it is customary to introduce various catalyst metals in the form of salts which have heat-decomposable anions or cations. For example, molybdenum is frequently introduced into such aqueous compositions in the form of ammonium molybdate, whereas elements such as iron, bismuth, cobalt, nickel and so forth are often times introduced in the form of nitrates. When an aqueous solution or slurry containing such salts is dried, the precipitate obtained contains not only the metals of the objective catalyst but also various heat-decomposable salts such as ammonium nitrate.
In normal catalyst preparations, the pre-catalyst precipitate is heated at an elevated temperature, e.g. 400.degree. C., for a period of about 1 to 4 hours before catalyst calcination. This pre-heating step serves to drive-off substantially all of the heat-decomposable ingredients such as nitrates, which might be present. Thereafter, the pre-heated pre-catalyst is calcined in the presence of oxygen to form a catalytic material of appropriate composition.
Catalytic materials produced in this manner are often times in the form of a very fine powder. Since powdery materials are normally unsuitable for use as fixed-bed catalysts, it is usually necessary to agglomerate the powder into large-sized particles or beads. Normally this is done by tableting, wherein a small amount of binder is mixed with the powder and the mixture so obtained formed into tablets by a suitable machine.
Although fixed-bed catalysts produced by this procedure may exhibit good catalytic properties, it would be beneficial if fixed-bed catalysts made from powders could be produced in such a way so as to have even better catalytic properties.
Accordingly, it is an object of the present invention to provide a novel catalyst preparation technique for forming fixed-bed catalysts with improved catalytic properties.